(i) Field of the Invention
The present invention relates to a hollow article made of a thermoplastic resin and having both end portions whose wall thickness changes multidirectionally with extremely high accuracy, such as tri-port type CV-joint boots for automobiles.
(ii) Description of the Related Art
Conventionally, as illustrated in FIG. 7 for example, a hollow article 8 such as a CV-joint boot for an automobile is known. In the CV-joint boot 8, one end portion (the upper end portion in FIG. 7) 40 has been formed by injection molding and all other portions have been formed by blow molding. As an apparatus for manufacturing such a hollow article 8, an apparatus illustrated in FIG. 6 is known (Japanese Patent No. 2556647).
The apparatus illustrated in FIG. 6 is a parison manufacturing apparatus for blow-molding bellows (hollow article) 8, in which the bellows is blow-molded with its cross-sectional profile being changed into a wave shape through the whole length of a parison 18, as illustrated in FIG. 6. Since the circular parison 18 is never flatly compressed, the plastic is extended evenly throughout the whole periphery. This prior art is very superior for molding such bellows 8. In the bellows molded with this apparatus, since its one end portion (the upper end portion in FIG. 6) 40 is injection-molded with a neck mold, the thickness of that portion can be changed multidirectionally on the circumference with high accuracy. In the portion other than the one end portion 40, however, its thickness cannot but be uniform throughout the circumference because it is blow-molded. As a result, the apparatus can provide only such a general automobile CV-joint boot (bellows) 8 as illustrated in FIG. 7. This point is a problem of the prior art, which the present invention is to solve in particular. More specifically, some tri-port type CV-joint boots, for example, may require not only a high dimensional accuracy at the one end portion 40 (the wall thickness must be changed multidirectionally with high accuracy) but also a high dimensional accuracy at the other end portion (the lower end portion in FIG. 6) 41 (the inner circumference must be formed unevenly in height and the outer circumference must be formed into an accurate circle), that is, they may require an accurate shape at either of both end portions of the bellows, whose wall thickness is changed multidirectionally. The above-described prior art, however, has a problem that it can not meet this requirement. Further, in case of a conventional automobile CV-joint boot (FIG. 7) made with a manufacturing apparatus of this kind, the molded portion from the distal end of a nozzle mouthpiece 2 to the other end 41 of the CV-joint boot is an unnecessary portion, and such an unnecessary portion is very large. This brings about a problem that a great deal of waste is generated. On the other hand, Japanese Patent Application Laid-open No. 10-272679 discloses a method in which, upon injection-blow molding, the mold for the final product shape portion (portion corresponding to the other end portion 41 in the above-described prior art) is not changed for injection molding and for blow molding and it is successively molded, and thereby no flash is generated and the dimensional accuracy is kept. By this technique, only the other end portion as the final product shape portion 41 meets the above-described object, but the one end portion (portion corresponding to the one end portion 40 in the above-described prior art) is blow-molded by changing an injection mold and a blow mold with each other. Therefore, even by this technique, a configuration in which the wall thickness at both ends is changed multidirectionally with high accuracy can not be formed. So, as a result of repeating earnest studies and examinations, by improving the manufacturing apparatus of the above-described prior art (Japanese Patent No. 2556647), the present applicant has succeeded in newly developing a hollow article made of a thermoplastic resin and having both end portions whose wall thickness changes multidirectionally with extremely high accuracy, a manufacturing method of the hollow article, and a manufacturing apparatus for the hollow article.
The present invention has been developed in view of such problems of the prior art, and its object is to provide a hollow article made of a thermoplastic resin and having both end portions whose wall thickness changes multidirectionally with extremely high accuracy.
Technical measures made by the present invention to solve the above problems are as follows. A hollow article made of a thermoplastic resin is formed by bringing a cavity of a drawing unit into contact with an outlet gap of an annular orifice nozzle made up of a nozzle core constituted so as to be upwardly and downwardly movable, and a nozzle mouthpiece concentrically surrounding said core to form said outlet gap having a variable gap width for upward extruding the thermoplastic resin between it and said core; injecting the thermoplastic resin into said cavity through said outlet gap to form one end portion having a configuration in which a wall thickness changes multidirectionally with extremely high accuracy; drawing and forming a tubular parison while moving said drawing unit apart from said annular orifice; blow-molding the tubular parison after replacing an uppermost portion of said nozzle mouthpiece constituting said outlet gap with a blow mold to form a hollow article body; injection-molding the other end portion of a hollow article having a configuration in which a wall thickness changes multidirectionally with extremely high accuracy, through a cavity having a desired shape of said nozzle mouthpiece at a lower portion; and laterally moving said blow mold and said nozzle mouthpiece upon taking out a product to open them. A typical example of the hollow article is a tri-port type CV-joint boot for an automobile.
A manufacturing apparatus for the hollow article is as follows.
The apparatus comprises an annular orifice nozzle made up of a nozzle core constituted so as to be upwardly and downwardly movable, and a nozzle mouthpiece concentrically surrounding said core to form an outlet gap having a variable gap width for upward extruding a thermoplastic resin between it and said core; a drawing unit having a cavity of a desired shape downward opened for forming one end portion of a hollow article, said drawing unit being moved apart from said annular orifice nozzle to draw and form a tubular parison after injecting the thermoplastic resin into said cavity on said outlet gap of said annular orifice nozzle; and a blow mold for blow-molding said tubular parison to form a hollow article body of a desired shape, wherein said nozzle mouthpiece is multi-divided vertically and laterally, each divided part is disposed so as to be able to reciprocate laterally, an uppermost portion of said nozzle mouthpiece divided is constituted so as to be replaceable with said blow mold upon blow molding, and a lower portion of said nozzle mouthpiece has a desired cavity and said blow mold and said nozzle mouthpiece can be moved laterally upon taking out a product after forming the other end portion of the hollow article into a desired shape to open them. The above nozzle mouthpiece is divided into at least a portion for forming the outlet gap, and a portion for injection-molding the other end portion of the hollow article having a configuration in which a wall thickness changes multidirectionally with extremely high accuracy.
The nozzle mouthpiece multi-divided vertically and laterally can have an individual independent temperature conditioning system to set the thermoplastic resin in the nozzle mouthpiece at a proper temperature any time.
A manufacturing method of the above hollow article comprises the steps of bringing a cavity of a drawing unit into contact with an outlet gap of an annular orifice nozzle made up of a nozzle core constituted so as to be upwardly and downwardly movable, and a nozzle mouthpiece concentrically surrounding said core to form said outlet gap having a variable gap width for upward extruding a thermoplastic resin between it and said core; injecting the thermoplastic resin into said cavity through said outlet gap to form one end portion having a configuration in which a wall thickness changes multidirectionally with extremely high accuracy; drawing and forming a tubular parison while moving said drawing unit apart from said annular orifice; blow-molding the tubular parison after replacing an uppermost portion of said nozzle mouthpiece constituting said outlet gap with a blow mold to form a hollow article body; injection-molding the other end portion of a hollow article having a configuration in which a wall thickness changes multidirectionally with extremely high accuracy, with a cavity having a desired shape at a lower portion of said nozzle mouthpiece; and then laterally moving said blow mold and said nozzle mouthpiece upon taking out a product to open them, thereby forming a hollow article having both end portions whose wall thickness changes multidirectionally with extremely high accuracy.
In the present invention, the shape of the one end portion is determined by the cavity shape of the neck mold. On the other hand, the shape of the other end portion is determined by that the cavity (space shape) defined by the nozzle mouthpiece of the annular orifice nozzle and the outer side surface of the nozzle core serves as a flow passage for the thermoplastic resin when pushing into the neck mold and when extruding the parison, and keeps the thermoplastic resin filling up the lower portion of the space shape upon blow molding. At this time, the thermoplastic resin filling up the upper portion of the annular orifice nozzle is expanded to the inner wall surface of the blow mold by compressed gas blown into the parison after part of the upper portion of the nozzle mouthpiece is replaced with the blow mold while keeping the nozzle core intact, and the shapes of the parison and the other end become one continuous body. This makes it possible to manufacture such a hollow article made of a thermoplastic resin and having both end portions whose wall thickness changes multidirectionally with extremely high accuracy. Further, in case of, e.g., an automobile CV-joint boot made with this manufacturing apparatus, in which the outer diameter of the other end is larger than that of the one end, the unnecessary molded portion from the distal end of the nozzle mouthpiece to the other end portion of the CV-joint boot becomes small and there is an advantage that the amount of waste generated becomes very little. Here, the nozzle mouthpiece multi-divided vertically and laterally can have an individual independent temperature conditioning system, and it can be adjusted and set at temperatures at which the thermoplastic resin in the nozzle mouthpiece is made easy to flow upon flowing, easy to blow upon blowing, and solidified at a short time.
The present invention provides not only the manufacturing apparatus of the hollow article but also a method for molding a specific hollow article by manufacturing a specific parison and a specific shape using a specific apparatus. In this respect, the present invention can also make it possible to, for example, first push a thermoplastic resin into a cavity of a neck mold in contact with an annular orifice nozzle for plastic, then form a parison with moving said neck mold apart from said annular orifice nozzle, said parison being a tubular parison having various different cross-sections throughout the whole length of the parison so that the wall thickness of the parison formed may change into a wave shape through troughs and peaks, operate a controller for a drive unit for moving the neck mold onto/apart and a controller for a drive unit for changing plastic flowing out through an outlet gap of said annular orifice nozzle, while moving the neck mold apart from said annular orifice nozzle, said outlet gap of said annular orifice nozzle being changed in accordance with the quantity of the plastic flowing out, increase the speed of said neck mold from zero when moving the neck mold apart from said annular orifice nozzle, and operate both controllers as described above to work in the period when said neck mold is further moving apart. Here, the characteristic features of the present invention are in that the nozzle mouthpiece constituting the annular orifice nozzle is multi-divided vertically and laterally, each divided portion is disposed so as to be able to reciprocate laterally, part of the upper portion of the nozzle mouthpiece is replaced with the blow mold, and further, part lower than that keeps the thermoplastic resin filling up also upon blowing and is made to be able to open and close for taking out a product, and thereby, a hollow article is formed having both end portions whose wall thickness changes multidirectionally with extremely high accuracy.
A hollow article of the present invention can be constructed in consideration of various use objects. Besides, the manufacturing method and the manufacturing apparatus for the hollow article of the present invention are particularly advantageous because they are constructed so that they can manufacture tri-port type CV-joint boots. Such a boot is provided for use on the transmission side of an automobile, and it requires not only a high accuracy in dimension of one end portion but also, in the other end portion, an accurate configuration in which the wall thickness changes multidirectionally, i.e., the profile of the outer periphery must be made into an accurate circle while protrusions are formed on the inner peripheral side. Important points when using it are not only the point that the bellows manufactured according to the present invention is made of a thermoplastic elastomer, but also in that high accurate bellows both end portions can be obtained because it can be manufactured with more accuracy by setting the neck mold, the annular orifice nozzle, and the divided nozzle mouthpiece.